Looking ahead: echolocation and flight behaviors of two fruit bat species navigating a corridor

Bats navigating clutter must steer around obstacles to avoid collision, while simultaneously planning future flight trajectories. In this study, we investigated active sensing strategies of two bat species negotiating turns under matched geometric constraints. We compare the Egyptian fruit bat (Rousettus aegyptiacus), a lingual echolocator that can actively direct its sonar beam axis using tongue driven mechanisms, and the short-tailed fruit bat (Carollia perspicillata), a laryngeal nasal echolocator whose head aim and nose leaf shape emission directionality. Bats flew through a felt lined, 'L' shaped corridor designed to elicit turns. A 32-channel ultrasonic array and 3D video tracking system captured their sonar emissions and flight trajectories. In both species, bats reduced flight speeds and increased angular deviation between sonar beam aim (acoustic gaze) and flight direction before the apex of high angle turns. A directional prediction analysis showed that sonar gaze reliably anticipated the direction of the subsequent heading change in both species (77% in R. aegyptiacus; 70% in C. perspicillata). However, baseline flight and echolocation behavior differed between species: C. perspicillata flew faster and, produced higher sonar pulse rates than R. aegyptiacus, consistent with species differences in body size, wing morphology, and sensory ecology. Together, these data demonstrate that fruit bats prospectively orient acoustic gaze to guide upcoming trajectory changes, extending "steering by hearing" beyond prey tracking by insectivorous bats to navigation of cluttered space by frugivorous bats.